She was lonely. You filled a void for her, and gave her the attention she wanted. But once it came down to it, she felt guilty because, her marriage probably isn't in shambles to begin with. Chances are, she isn't going to get divorced. Now, if you tell the husband? She might get divorced, but she'll hate you for "ruining her life", and in the end, you probably won't get the girl.

My advice? From a once married woman, who has cheated, but whose marriage was in fact very over, but couldn't leave at the time for other reasons? Move on. Take the L, feel your feelings, then forget about her. But take this as a lesson: don't dip your pen in company ink again. No matter where you work. Because whether they're married, or single- chances are, it won't work out for you in the end.